Vehicles such as school buses serve to pick up and discharge passengers. When passengers are discharged from the front door of the bus to the side of a road, the passengers may attempt to cross the road immediately in front of the bus. This poses a safety risk, particularly with school-age children, as the road immediately in front of the bus may be in the bus driver's blind spot, i.e. outside the bus driver's range of vision. Accordingly, safety measures such as crossing gates mounted on the front of the bus have been employed for many years. An example is shown in U.S. patent application Ser. No. 5,406,250 issued Apr. 11, 1995 to Reavell et al., which is incorporated herein by reference.
These crossing gates are typically hinged to the front of the bus at the side nearest the front door. In the retracted state, the crossing gate is held parallel to the front of the bus. When the bus stops and the front door is opened, the crossing gate is extended until it is substantially perpendicular to the front of the bus, effectively providing a barrier at the side of the road of typically at least six feet. Discharged passengers who wish to cross the road must walk around the crossing gate, causing them to pass through the driver's range of vision. After the passengers have passed beyond the front of the bus, the crossing gate is retracted.
An example of a prior art retraction mechanism is U.S. Pat. No. 4,816,804 issued Mar. 28, 1989 to Reavell, which is incorporated herein by reference. The apparatus controlling the safety device, in the case of U.S. Pat. No. 4,816,804 a school bus stop sign, is automatically responsive to the opening and closing of the bus door such that when the door is opened, the apparatus swings the hinged sign to its extended position, and when the door is closed, the apparatus returns the sign to its retracted position. The apparatus comprises a unidirectional motor coupled to the hinged sign through an eccentric drive and a link arm. The link arm is provided with a preloaded, helical compression spring which absorbs the shock of mechanical leverage.
However, apparatus such as these do not prevent inadvertent deployment of the safety device. Although a compression spring in the link arm can help to prevent excessive forces from damaging the mechanical linkages on the safety device, it is not able to prevent unintended deployment of the safety device when the device is exposed to high winds. Wind may catch the safety device, especially in the case of a gate, and partially or fully deploy the gate or even damage the device. Particularly if the bus is in motion, such accidental deployment of the gate is a significant hazard. Even when the bus is parked, the gate is more susceptible to breakage and damage from high winds when extended inadvertently.
One solution to this problem has been to employ a magnetic device to hold or assist in holding a crossing gate in the retracted position. The magnet provides an advantage over mechanical holding devices, since there are no moving parts exposed to the elements and therefore the durability of a magnetic holding device is significantly greater than that of a mechanical holding device.
However, problems arise in the deployment of the gate to an extended position. In the case of a reciprocating arm which is of significant length, which is typical of a safety gate, it is difficult for the motor which moves the crossing arm to provide sufficient force to overcome the magnetic forces, so an electromagnetic device capable of deactivation must be used in order that the crossing gate can be released at the appropriate time to allow for extension of the crossing gate. Since the electromagnetic device is energized whenever the crossing gate is in the retracted position, in order to increase holding power of the crossing gate, the lifespan of the electromagnet is curtailed and the power supply is drained. This is not a satisfactory solution for use when the bus is not in operation and the power is shut off and parked, for example where high winds or storms strike overnight.
It would accordingly be advantageous to provide an electromagnetic device for engaging a reciprocating arm such as a safety gate which readily allows for the release of an arm of the safety gate from a retracted position. It would also be advantageous to provide a device for engaging a reciprocating arm such as a safety gate in a retracted position by a permanent magnetic device which does not require a constant power source when the reciprocating arm is in the retracted position. It would further be advantageous to provide a device for engaging a reciprocating arm such as a safety gate by a permanent magnetic device which is integrated with the operation of another safety gate such as a stop arm.